This laboratory studies the role of the skin as an immunological organ. We study the mechanisms involved in delayed type hypersensitivity (DTH) reactions in the skin and use this knowledge to better understand lymphocyte- mediated skin diseases. In the past year we have continued to focus our studies on 1) the immune elements of the epidermis and dermis and on their interactions with the rest of the immune system, 2) the identification and characterization of mast cell precursors in fetal skin, and 3) the development of a model that may provide insight into mechanisms involved in autoimmune reactions in skin and in the maintainance of tolerance to epidermally-derived proteins. We have attempted to delineate whether and how CD4+ T cell responses could be skewed toward Th1 or Th2 rich reactions. We found that a relative skewing of a T cell response can occur as a consequence of immunization with various types of adjuvants. We also continue to try to skew these inflammatory responses using gene transfer into bone marrow derived dendritic cells (BMDC). In this regard, we have characterized the ability of antigen-pulsed BMDC to induce various types of DTH reactions and are now attempting to utilize these cells as vehicles for gene vaccination experiments. We have also completed a study that demonstrates that LC express FasL after activation triggered through CD40 molecules on their surface, but not by stimulation with LPS or IFNg. These studies suggest a new feedback mechanism to downregulate T cell activation by LC through the interaction of the TNF receptor/ligand superfamily, CD40/CD40L and Fas/FasL. In characterizing the infiltrates of day 16 fetal skin we found that many of the cells represent immature mast cells. Under certain culture conditions these cells could proliferate and become mature mast cells. This novel culture method has enabled us to follow and characterize mast cells throughout development. The studies were facilitated by finding that the mAb DX5 bound not only to NK cells but also to fetal skin mast cells as well as to connective tissue mast cells. These cells were distinct from bone marrow derived mast cells. The third project that we are pursuing involves the development of a model of skin autoimmunity and tolerance induction. We are crossing mice that have a TCR transgene that recognizes ovalbumin in association with H-2b (OT-I) with mice that have been generated with a K14-ovalbumin (K-14 OVA) encoding gene. These mice have the TCR for ovalbumin and express ovalbumin in the epidermis but have no apparent disease. Preliminary studies indicate that these mice are depleted of CD8 cells that have the TCR transcripts. We are also using the K-14 OVA mice as targets for immunological reactions in the skin. We are currently injecting T cells from OT-I mice and assessing their role in causing inflammatory skin lesions. We have now also begun breeding OT-II mice (that have a TCR that recognizes OVA paptides in Class II MHC molecules) and will characterize any abnormalities that occur when cells from these mice are infused into the K-14 OVA mice.